Decoder and decoding method selecting an error concealment mode, and encoder and encoding method

ABSTRACT

A decoder for decoding a frame to reconstruct a signal portion of a signal is provided. The signal portion is encoded within the frame, wherein the frame includes a bitstream payload and two or more redundancy bits, wherein the bitstream payload includes a plurality of payload bits, wherein each of the payload bits exhibits a position within the bitstream payload. The decoder includes a channel decoding module, being configured to detect, depending on the two or more redundancy bits, whether the bitstream payload includes one or more corrupted bits being one or more of the payload bits that are distorted or that are likely to be distorted. Moreover, the decoder includes a source decoding module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending InternationalApplication No. PCT/EP2020/053618, filed Feb. 12, 2020, which isincorporated herein by reference in its entirety, and additionallyclaims priority from European Applications Nos. EP 19157042.3, filedFeb. 13, 2019, EP 19156997.9, filed Feb. 13, 2019, EP 19157036.5, filedFeb. 13, 2019, and EP 19157047.2, filed Feb. 13, 2019, and InternationalApplications Nos. PCT/EP2019/065209, filed Jun. 11, 2016,PCT/EP2019/065205, filed Jun. 11, 2016, and PCT/EP2019/065172, filedJun. 11, 2016, which are all incorporated herein by reference in theirentirety.

The present invention relates to a decoder and a decoding methodselecting an error concealment mode, and to an encoder and to anencoding method.

BACKGROUND OF THE INVENTION

Bit-errors can occur on the transmission chain between the encoder andthe decoder.

Untreated bit-errors can lead to annoying artefacts; therefore, manyaudio decoders just simply trigger frame loss/packet loss concealment(PLC) on a full frame, subsequently referred to as full frame lossconcealment (FFLC), if any bit-error is detected within this frame.Often, this achieves a good audio quality, especially when the signal isstationary.

MPEG-4 Part 3 Audio [1] defines error sensitivity categories for thebitstream payload of AAC (Table 4.94); Table 1 shows the categories forthe AAC main data. In particular, table 1 depicts error sensitivitycategories for AAC.

TABLE 1 leads/may lead to one category Payload mandatory instance perDescription 0 Main yes CPE/ commonly used side stereo layer information1 main yes ICS channel dependent side information 2 main no ICS errorresilient scale factor data 3 main no ICS TNS data 4 main yes ICSspectral data

Depending on the distorted classes, individual concealment strategiesare chosen as denoted in Table 2. Table 2 depicts concealment strategiesfor AAC error sensitivity categories.

TABLE 2 Category Concealment strategy 0 Frame loss concealment 1 Channelconcealment (in case of multi− channel signals) 2 Conceal just thespectral lines of distorted scale factor bands [2] 3 Do not apply TNS incase of bit-errors 4 Decode spectrum regardless of bit-errors

MPEG-4 Part 3 Audio also specifies Bit Sliced Arithmetic Coding (BSAC),which allows fine-grain scalability with a high number of layers. Toimprove the error resilience, Segmented Binary Arithmetic (SBA) Codingwas introduced, which groups multiple layers into segments. Arithmeticcoding is re-initialized at the beginning of each segment to circumventerror propagation.

An adaptive selection of time-domain or frequency-domain concealment isproposed in [3]. In [3], three error detection methods are described.

A first error detection method uses a cyclic redundancy check (CRC).

A second error detection method compares the length of a bitstreampayload as transmitted from an encoder with the length of the bitstreampayload given to the decoder.

A third error detection method compares the length of a bitstreampayload as transmitted from an encoder with the length of the consumedbits during the decoding process of the bitstream payload: In BSAC, 32additional bits or less can be decoded due to characteristics of thearithmetic decoding. Therefore, if the bit difference is more than 32bits, it is determined that an error exists.

Subsequently in [3], a plurality of error location methods aredescribed:

According to a first error location method of [3], a comparison ofspectral energy of the current frame with that of the previous frame isconducted.

According to a second error location method of [3], an examination ofbits allocated to each layer of the decoded bitstream payload relativeto the number of bits consumed by the arithmetic decoder is conducted.When errors exist in a layer, more or less bits might be used in thearithmetic decoding. Therefore, a layer using more or less bitsindicates a high possibility that errors exist in this layer or in aprevious layer.

Following up on this location, different concealment strategies aresuggested in [3]: If the detected position is before a first criticalposition, time domain concealment is applied. If the detected positionis after a first critical position, but before a second criticalposition, frequency domain concealment is applied. If the detectedposition is after a second critical position, concealment is notapplied.

Various frame loss concealment techniques available in the frequencydomain are discussed in [4]. In particular, muting, repetition, noisesubstitution and prediction are mentioned in [4].

SUMMARY

According to an embodiment, a decoder for decoding a frame toreconstruct a signal portion of a signal, wherein the signal portion isencoded within the frame, wherein the frame includes a bitstream payloadand two or more redundancy bits, wherein the bitstream payload includesa plurality of payload bits, wherein each of the payload bits exhibits aposition within the bitstream payload, may have: a channel decodingmodule, being configured to detect, depending on the two or moreredundancy bits, whether the bitstream payload includes one or morecorrupted bits being one or more of the payload bits that are distortedor that are likely to be distorted, a source decoding module, wherein,if the channel decoding module has not detected any corrupted bitswithin the bitstream payload, the source decoding module is configuredto decode the bitstream payload without conducting error concealment toreconstruct the signal portion, wherein, if the channel decoding modulehas detected the one or more corrupted bits within the bitstreampayload, the source decoding module is configured to select a selectederror concealment mode of two or more error concealment modes dependingon the position of at least one of the one or more corrupted bits withinthe bitstream payload and depending on a signal characteristic of thesignal portion of the signal, and is configured to conduct errorconcealment depending on the selected error concealment mode toreconstruct the signal portion.

According to another embodiment, a system may have: an encoder forencoding a signal portion of a signal within a frame, wherein theencoder is configured to generate the frame so that the frame includes abitstream payload and two or more redundancy bits, wherein the bitstreampayload includes a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, and aninventive decoder.

According to another embodiment, an encoder may have: a source encodingmodule for encoding a signal portion of a signal within a frame, whereinthe source encoding module is configured to generate the frame so thatthe frame includes a bitstream payload and two or more redundancy bits,wherein the bitstream payload includes a plurality of payload bits,wherein each of the payload bits exhibits a position within thebitstream payload, wherein the frame being generated by the sourceencoding module is suitable for being processed by the inventivedecoder, and a channel encoding module being configured to generate thetwo or more redundancy bits depending on the bitstream payload.

According to another embodiment, a method for decoding a frame toreconstruct a signal portion of a signal, wherein the signal portion isencoded within the frame, wherein the frame includes a bitstream payloadand two or more redundancy bits, wherein the bitstream payload includesa plurality of payload bits, wherein each of the payload bits exhibits aposition within the bitstream payload, may have the steps of:

detecting, depending on the two or more redundancy bits, whether thebitstream payload includes one or more corrupted bits being one or moreof the payload bits that are distorted or that are likely to bedistorted, if no corrupted bits have been detected within the bitstreampayload, decoding the bitstream payload without conducting errorconcealment to reconstruct the signal portion, and if one or morecorrupted bits have been detected within the bitstream payload,selecting a selected error concealment mode of two or more errorconcealment modes depending on the position of at least one of the oneor more corrupted bits within the bitstream payload and depending on asignal characteristic of the signal portion of the signal, andconducting error concealment depending on the selected error concealmentmode to reconstruct the signal portion.

According to another embodiment, a method may have the steps of:encoding a signal portion of a signal within a frame, wherein the frameis generated so that the frame includes a bitstream payload and two ormore redundancy bits, wherein the bitstream payload includes a pluralityof payload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, and conducting the method for decoding aframe to reconstruct a signal portion of a signal, wherein the signalportion is encoded within the frame, wherein the frame includes abitstream payload and two or more redundancy bits, wherein the bitstreampayload includes a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, whereinthe method may have the steps of: detecting, depending on the two ormore redundancy bits, whether the bitstream payload includes one or morecorrupted bits being one or more of the payload bits that are distortedor that are likely to be distorted, if no corrupted bits have beendetected within the bitstream payload, decoding the bitstream payloadwithout conducting error concealment to reconstruct the signal portion,and if one or more corrupted bits have been detected within thebitstream payload, selecting a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and conducting error concealment depending on the selected errorconcealment mode to reconstruct the signal portion, using the frame.

According to another embodiment, a method for encoding a signal portionof a signal within a frame may have the steps of: generating the frameso that the frame includes a bitstream payload and two or moreredundancy bits, wherein the bitstream payload includes a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, wherein the frame is suitable for beingdecoded by the method for decoding a frame to reconstruct a signalportion of a signal, wherein the signal portion is encoded within theframe, wherein the frame includes a bitstream payload and two or moreredundancy bits, wherein the bitstream payload includes a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, wherein the method may have the steps of:detecting, depending on the two or more redundancy bits, whether thebitstream payload includes one or more corrupted bits being one or moreof the payload bits that are distorted or that are likely to bedistorted, if no corrupted bits have been detected within the bitstreampayload, decoding the bitstream payload without conducting errorconcealment to reconstruct the signal portion, and if one or morecorrupted bits have been detected within the bitstream payload,selecting a selected error concealment mode of two or more errorconcealment modes depending on the position of at least one of the oneor more corrupted bits within the bitstream payload and depending on asignal characteristic of the signal portion of the signal, andconducting error concealment depending on the selected error concealmentmode to reconstruct the signal portion, and generating the two or moreredundancy bits depending on the bitstream payload.

Another embodiment may have a non-transitory digital storage mediumhaving a computer program stored thereon to perform any of the inventivemethods when said computer program is run by a computer.

Another embodiment may have a frame being generated according to themethod for encoding a signal portion of a signal within a frame, whereinthe method may have the steps of: generating the frame so that the frameincludes a bitstream payload and two or more redundancy bits, whereinthe bitstream payload includes a plurality of payload bits, wherein eachof the payload bits exhibits a position within the bitstream payload,wherein the frame is suitable for being decoded by the method fordecoding a frame to reconstruct a signal portion of a signal, whereinthe signal portion is encoded within the frame, wherein the frameincludes a bitstream payload and two or more redundancy bits, whereinthe bitstream payload includes a plurality of payload bits, wherein eachof the payload bits exhibits a position within the bitstream payload,wherein the method may have the steps of: detecting, depending on thetwo or more redundancy bits, whether the bitstream payload includes oneor more corrupted bits being one or more of the payload bits that aredistorted or that are likely to be distorted, if no corrupted bits havebeen detected within the bitstream payload, decoding the bitstreampayload without conducting error concealment to reconstruct the signalportion, and if one or more corrupted bits have been detected within thebitstream payload, selecting a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and conducting error concealment depending on the selected errorconcealment mode to reconstruct the signal portion, and generating thetwo or more redundancy bits depending on the bitstream payload.

A decoder for decoding a frame to reconstruct a signal portion of asignal is provided. The signal portion is encoded within the frame,wherein the frame comprises a bitstream payload and two or moreredundancy bits, wherein the bitstream payload comprises a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload. The decoder comprises a channel decodingmodule, being configured to detect, depending on the two or moreredundancy bits, whether the bitstream payload comprises one or morecorrupted bits being one or more of the payload bits that are distortedor that are likely to be distorted. Moreover, the decoder comprises asource decoding module. If the channel decoding module has not detectedany corrupted bits within the bitstream payload, the source decodingmodule is configured to decode the bitstream payload without conductingerror concealment to reconstruct the signal portion. If the channeldecoding module has detected the one or more corrupted bits within thebitstream payload, the source decoding module is configured to select aselected error concealment mode of two or more error concealment modesdepending on the position of at least one of the one or more corruptedbits within the bitstream payload and depending on a signalcharacteristic of the signal portion of the signal, and is configured toconduct error concealment depending on the selected error concealmentmode to reconstruct the signal portion.

Moreover, an encoder is provided. The encoder comprises a sourceencoding module for encoding a signal portion of a signal within aframe, wherein the source encoding module is configured to generate theframe so that the frame comprises a bitstream payload and two or moreredundancy bits, wherein the bitstream payload comprises a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, wherein the frame being generated by thesource encoding module is suitable for being processed by theabove-described decoder. Furthermore, the encoder comprises a channelencoding module being configured to generate the two or more redundancybits depending on the bitstream payload.

Furthermore, a method for decoding a frame to reconstruct a signalportion of a signal is provided. The signal portion is encoded withinthe frame, wherein the frame comprises a bitstream payload and two ormore redundancy bits, wherein the bitstream payload comprises aplurality of payload bits, wherein each of the payload bits exhibits aposition within the bitstream payload. The method comprises:

-   -   Detecting, depending on the two or more redundancy bits, whether        the bitstream payload comprises one or more corrupted bits being        one or more of the payload bits that are distorted or that are        likely to be distorted.    -   If no corrupted bits have been detected within the bitstream        payload, decoding the bitstream payload without conducting error        concealment to reconstruct the signal portion, and    -   If one or more corrupted bits have been detected within the        bitstream payload, selecting a selected error concealment mode        of two or more error concealment modes depending on the position        of at least one of the one or more corrupted bits within the        bitstream payload and depending on a signal characteristic of        the signal portion of the signal, and conducting error        concealment depending on the selected error concealment mode to        reconstruct the signal portion.

Moreover, another method is provided. The method comprises:

-   -   Encoding a signal portion of a signal within a frame, wherein        the encoder is configured to generate the frame so that the        frame comprises a bitstream payload and two or more redundancy        bits, wherein the bitstream payload comprises a plurality of        payload bits, wherein each of the payload bits exhibits a        position within the bitstream payload. And:    -   Conducting, using the frame, the above-described method for        decoding the frame.

Furthermore, a method for encoding a signal portion of a signal within aframe is provided. The method comprises:

-   -   Generating the frame so that the frame comprises a bitstream        payload and two or more redundancy bits, wherein the bitstream        payload comprises a plurality of payload bits, wherein each of        the payload bits exhibits a position within the bitstream        payload, wherein the frame is suitable for being decoded by the        above-described method for decoding the frame. And:    -   Generating the two or more redundancy bits depending on the        bitstream payload.

Moreover, computer program for implementing one of the above describedmethods is provided when said method is executed on a computer or signalprocessor.

Furthermore, a frame being generated according to the above-describedmethod for encoding a signal portion of a signal within a frame isprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be detailed subsequentlyreferring to the appended drawings, in which:

FIG. 1 illustrates a decoder for decoding a frame to reconstruct asignal portion of a signal according to an embodiment.

FIG. 2 illustrates an encoder according to an embodiment.

FIG. 3 illustrates a system according to an embodiment.

FIG. 4 illustrates an example for analysing payload data of code wordsaccording to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a decoder 100 for decoding a frame to reconstruct asignal portion of a signal according to an embodiment.

The signal portion is encoded within the frame, wherein the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload.

The decoder 100 comprises a channel decoding module 110, beingconfigured to detect, depending on the two or more redundancy bits,whether the bitstream payload comprises one or more corrupted bits beingone or more of the payload bits that are distorted or that are likely tobe distorted.

Moreover, the decoder 100 comprises a source decoding module 120.

If the channel decoding module 110 has not detected any corrupted bitswithin the bitstream payload, the source decoding module 120 isconfigured to decode the bitstream payload without conducting errorconcealment to reconstruct the signal portion.

If the channel decoding module 110 has detected the one or morecorrupted bits within the bitstream payload, the source decoding module120 is configured to select a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and is configured to conduct error concealment depending on theselected error concealment mode to reconstruct the signal portion.

According to an embodiment, the channel decoding module may, e.g., be anerror detection and error correction module being configured to conducterror correction on the bitstream payload before detecting whether thebitstream payload comprises the one or more corrupted bits.

In an embodiment, if the channel decoding module 110 determines that itcannot successfully conduct the error correction on the bitstreampayload, the channel decoding module 110 may, e.g., be configured todetermine said one or more corrupted bits within the bitstream payload.

According to an embodiment, a first one of the two or more errorconcealment modes may, e.g., be a full frame loss concealment mode. Ifthe channel decoding module 110 has indicated that the bitstream payloadcomprises the one or more corrupted bits, and if the selected errorconcealment mode is the full frame loss concealment mode, the sourcedecoding module 120 may, e.g., be configured to conduct errorconcealment without using the bitstream payload.

In an embodiment, a second one of the two or more error concealmentmodes may, e.g., be a partial frame loss concealment mode. If thechannel decoding module 110 has indicated that the bitstream payloadcomprises the one or more corrupted bits, and if the selected errorconcealment mode is the partial frame loss concealment mode, the sourcedecoding module 120 may, e.g., be configured to obtain the decodedsignal by decoding other bits of the payload bits that are not indicatedby the channel decoding module 110 to be the one or more corrupted bitswithout conducting error concealment on the other bits, and byconducting error concealment on the one or more of the payload bits thatare indicated by the channel decoding module 110 to be the one or morecorrupted bits.

According to an embodiment, the two or more error concealment modes maye.g., comprise exactly two error concealment modes, wherein a first oneof the exactly two error concealment modes may, e.g., be the full frameloss concealment mode, wherein a second one of the exactly two errorconcealment modes is the partial frame loss concealment mode.

In an embodiment, the bitstream payload may, e.g., be partitioned into afirst part of the plurality of payload bits of the bitstream payload,and into a second part of the plurality of payload bits of the bitstreampayload. If the channel decoding module 110 has indicated that thebitstream payload comprises the one or more corrupted bits, and if thefirst part of the bitstream payload comprises at least one of the one ormore corrupted bits, the source decoding module 120 may, e.g., beconfigured to select the full frame loss concealment mode as theselected error concealment mode. If the channel decoding module 110 hasindicated that the bitstream payload comprises the one or more corruptedbits, and if the first part of the bitstream payload does not compriseany of the one or more corrupted bits, the source decoding module 120may, e.g., be configured to select the selected error concealment modedepending on the signal characteristic of the signal portion of thesignal.

According to an embodiment, the frame is a current frame, wherein thebitstream payload is a current bitstream payload, wherein the pluralityof payload bits is a plurality of current payload bits, wherein thesignal portion of the signal is a current signal portion of the signal,and wherein the signal characteristic is a current signalcharacteristic. If the channel decoding module 110 has indicated thatthe current bitstream payload comprises the one or more corrupted bits,the source decoding module 120 may, e.g., be configured to select theselected error concealment mode of two or more error concealment modesdepending on the current signal characteristic of the current signalportion of the signal being encoded by the plurality of current payloadbits of the current frame, and depending on a previous signalcharacteristic of a previous signal portion of the signal being encodedby a plurality of previous payload bits of a previous bitstream payloadof a previous frame.

In an embodiment, the current signal portion of the signal being encodedby the plurality of current payload bits of the current bitstreampayload may, e.g., be a current audio signal portion of an audio signal,and the previous signal portion of the signal being encoded by theplurality of previous payload bits of the previous bitstream payloadmay, e.g., be a previous audio signal portion of the audio signal. Thecurrent bitstream payload may, e.g., encode a plurality of spectrallines of the current audio signal portion.

In an embodiment, if the corrupted bits only affect the residual bits,then no error concealment is done and the frame is decoded as normalframe without considering the corrupted residual bits.

A stability factor represents the similarity between two signals, forexample, between the current signal and a past signal. For example, thestability factor may, e.g., be bounded by [0:1]. A stability factorclose to 1 or 1 may, e.g., mean that both signals are very similar and astability factor close to 0 or 0 may, e.g., mean that both signals arevery different. The similarity may, for example, be calculated on thespectral envelopes of two audio signals.

In an embodiment, full frame loss concealment is conducted, if astability factor is lower than a threshold, for example, a threshold0.5.

According to an embodiment, if the channel decoding module 110 hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module 120 may, e.g., be configured to select the full frameloss concealment mode as the selected error concealment mode, if theprevious frame was concealed using full frame loss concealment.

In an embodiment, if the channel decoding module 110 has indicated thatthe current bitstream payload comprises the one or more corrupted bits,and if the first part of the current bitstream payload does not compriseany of the one or more corrupted bits, the source decoding module 120may, e.g., be configured to select the full frame loss concealment modeas the selected error concealment mode, if a highest spectral line amongthe plurality of spectral lines of the current audio signal portionexhibits a frequency being smaller than or equal to a thresholdfrequency.

According to an embodiment, if the channel decoding module 110 hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module 120 may, e.g., be configured to select the full frameloss concealment mode as the selected error concealment mode, if astability factor is smaller than a predefined threshold, wherein saidstability factor indicates a stability of the current audio signalportion and of the previous audio signal portion. For example, thepredefined threshold may, e.g., be equal to 0.5.

According to an embodiment, wherein, if the channel decoding module 110has indicated that the current bitstream payload comprises the one ormore corrupted bits, and if the first part of the current bitstreampayload does not comprise any of the one or more corrupted bits, thesource decoding module 120 may, e.g., be configured to select the fullframe loss concealment mode as the selected error concealment mode, ifthe previous frame was concealed using full frame loss concealment; orif a stability factor is smaller than a predefined threshold, whereinsaid stability factor indicates a stability of the current audio signalportion and of the previous audio signal portion. For example, thepredefined threshold may, e.g., be equal to 0.5.

In an embodiment, if the channel decoding module 110 has indicated thatthe current bitstream payload comprises the one or more corrupted bits,and if the first part of the current bitstream payload does not compriseany of the one or more corrupted bits, the source decoding module 120may, e.g., be configured to select the full frame loss concealment modeas the selected error concealment mode, if the highest spectral lineamong the plurality of spectral lines of the current audio signalportion represents said frequency being smaller than or equal to saidthreshold frequency, and if the first part of the current bitstreampayload encodes a signal component of the audio signal which is tonal orharmonic, and if the previous signal portion encodes at least one peakof the audio signal being greater than a peak threshold value and whichcorresponds to a frequency being greater than all frequencies beingindicated by the plurality of spectral lines of the current audio signalportion.

In another embodiment, a pitch of the audio signal may, e.g., exhibit apitch frequency. If the channel decoding module 110 has indicated thatthe current bitstream payload comprises the one or more corrupted bits,and if the first part of the current bitstream payload does not compriseany of the one or more corrupted bits, the source decoding module 120may, e.g., be configured to select the full frame loss concealment modeas the selected error concealment mode, if the highest spectral lineamong the plurality of spectral lines of the current audio signalportion represents said frequency being smaller than or equal to saidthreshold frequency, and if the first part of the current bitstreampayload encodes a signal component of the audio signal which is tonal orharmonic, and if all frequencies being indicated by the plurality ofspectral lines of the current audio signal portion are smaller than amaximal supported pitch frequency.

In an embodiment, full frame loss concealment is conducted, if thestability factor is higher than or equal to the threshold, for example,the threshold 0.5, and if the bitstream payload does not encode a signalcomponent of the audio signal which is tonal or harmonic, and if theratio between the energy from 0 to the frequency bin k_(be)−1 of theprevious quantized spectrum of the previous audio signal to the energyfrom 0 to the top of the previous quantized spectrum of the previousaudio signal is lower than a second threshold, for example, the secondthreshold 0.3.

According to an embodiment, if the channel decoding module 110 hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module 120 may, e.g., be configured to select the partial frameloss concealment mode as the selected error concealment mode, if theprevious frame was not concealed using full frame loss concealment, andif the highest spectral line among the plurality of spectral lines ofthe current audio signal portion exhibits a frequency being greater thansaid threshold frequency.

In an embodiment, if the channel decoding module 110 has indicated thatthe current bitstream payload comprises the one or more corrupted bits,and if the first part of the current bitstream payload does not compriseany of the one or more corrupted bits, the source decoding module 120may, e.g., be configured to select the partial frame loss concealmentmode as the selected error concealment mode, if the previous frame wasnot concealed using full frame loss concealment, and if the highestspectral line among the plurality of spectral lines of the current audiosignal portion exhibits said frequency being greater than said thresholdfrequency, and if said stability factor is greater than or equal to saidpredefined threshold, and if the first part of the current bitstreampayload does not encode a signal component of the audio signal which istonal or harmonic, and if the ratio between the energy from 0 to thefrequency bin k_(be)−1 of the previous quantized spectrum of theprevious audio signal to the energy from 0 to the top of the previousquantized spectrum of the previous audio signal is greater than or equalto said ratio threshold.

According to an embodiment, if the channel decoding module 110 hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module 120 may, e.g., be configured to select the partial frameloss concealment mode as the selected error concealment mode, if theprevious frame was not concealed using full frame loss concealment, andif the highest spectral line among the plurality of spectral lines ofthe current audio signal portion exhibits said frequency being greaterthan said threshold frequency, and if said stability factor is greaterthan or equal to said predefined threshold, if the first part of thecurrent bitstream payload encodes a signal component which is tonal orharmonic, and if said highest spectral line among the plurality ofspectral lines of the current audio signal portion exhibits a frequencybeing greater than the pitch frequency, and if the previous signalportion does not encode any peak of the audio signal being greater thansaid peak threshold value and which corresponds to said frequency beinggreater than all frequencies being indicated by the plurality ofspectral lines of the current audio signal portion.

In an embodiment, if the selected error concealment mode is the partialframe loss concealment mode, the source decoding module 120 may, e.g.,be configured to determine for each code word of a plurality of codewords of the second part of the bitstream payload, depending on a numberof corrected symbols of said code word, whether or not to conduct errorconcealment for those of the plurality of spectral lines of the currentaudio signal portion being represented by said code word, and to conducterror concealment for said those of the plurality of spectral lines ofthe current audio signal portion, for which the source decoding module120 has determined that error concealment shall be conducted.

According to an embodiment, for each code word of a plurality of codewords of the second part of the bitstream payload, the source decodingmodule 120 may, e.g., be configured to determine a risk value indicatingan approximation of a probability that said code word is corrupt, and todetermine whether or not said risk value is greater than a riskthreshold.

In an embodiment, the source decoding module 120 may, for example, beconfigured to determine the risk value further depending on a forwarderror correction coding mode.

According to an embodiment, the risk threshold may, e.g., be 2⁻¹⁶.

In other embodiments, another risk threshold may, e.g., be employed, forexample, 2⁻¹², or, for example, 2⁻¹⁸, or, for example, 2⁻²⁰.

In an embodiment, the source decoding module 120 may, e.g., beconfigured to calculate the risk value, for example, as follows:

${r\left( {m,\tau} \right)}:={16^{{- 2}{({m - 1})}}\begin{pmatrix}{14} \\\tau\end{pmatrix}1{5^{\tau}.}}$

wherein m indicates an epmode (e.g., the forward error correction codingmode), and wherein τ indicates a number of symbol errors (e.g., a numberof corrected symbols).

The above formula may, e.g., be valid for m=2, 3, 4 and τ=0, . . . ,m−1.

In other embodiments, the source decoding module 120 may, e.g., beconfigured to employ a lookup-table to determine the risk valuedepending on the number of symbol errors (e.g., the number of correctedsymbols), and depending on the epmode (e.g., the forward errorcorrection coding mode).

For example, in an embodiment, a lookup table as follows may, e.g., beemployed.

epmode\ error count 0 1 2 3 3 2^(∧) − 16 13385*2^(∧) − 22 20475*2^(∧) −16 not available 4 2^(∧) − 24 13385*2^(∧) − 30 20475*2^(∧) − 2419195*2^(∧) − 18

In the above example, when, for example, a risk threshold of 2⁻¹⁶ isemployed, it follows that in epmode 3, no errors are allowed, and inepmode 4, at most 1 error is allowed.

In other embodiments, the lookup table may take different values for therisk value, for the epmode and for the error count (for example, takingeven more errors 4, 5, 6, etc., or only fewer errors intoconsideration).

In other embodiments, the risk value may, e.g., be determined by thecodeword length or in another way.

For example, some embodiments may, e.g., employ a different calculationof the risk value, e.g.,

${{r\left( {m,\tau} \right)}:={12^{{- 2}{({m - 1})}}\begin{pmatrix}{14} \\\tau\end{pmatrix}16^{\tau}}},$

or, e.g.,

${r\left( {m,\tau} \right)}:={10^{{- 2}{({m - 1})}}\begin{pmatrix}{14} \\\tau\end{pmatrix}{8^{\tau}.}}$

Moreover, further embodiments may, e.g., only depend on the number ofsymbol errors but not on a forward error correction coding mode.

For example, in such embodiments, the risk value, may, e.g., becalculated as follows:

${{r\left( {m,\tau} \right)}:={16^{- 6}\begin{pmatrix}{14} \\\tau\end{pmatrix}15^{\tau}}},$

or according to

${{r\left( {m,\tau} \right)}:={8^{- 6}\begin{pmatrix}{14} \\\tau\end{pmatrix}14^{\tau}}},$

or according to

${r\left( {m,\tau} \right)}:={4^{- 6}\begin{pmatrix}{14} \\\tau\end{pmatrix}1{8^{\tau}.}}$

In an embodiment, if said risk value is greater than said riskthreshold, the source decoding module 120 may, e.g., be configured toconduct error concealment for those of the plurality of spectral linesof the current audio signal portion being represented by said code word.

In an embodiment, the source decoding module 120 is configured toconduct said error concealment for said code word is conducted in thepartial frame loss error concealment mode.

According to an embodiment, the channel decoding module 110 may, e.g.,be configured to detect that the bitstream payload comprises one or morecorrupted bits, if the channel decoding module 110 encounters anuncorrectable code word within the bitstream payload and/or if thechannel decoding module 110, after conducting error correction on aplurality of code words of the bitstream payload, determines are-calculated hash value, which depends on said plurality of code wordsafter the error correction, that differs from a received hash value.

FIG. 2 illustrates an encoder 150 according to an embodiment.

The encoder 150 comprises a source encoding module 160 for encoding asignal portion of a signal within a frame, wherein the source encodingmodule 160 is configured to generate the frame so that the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload, wherein the frame being generated by the source encoding module160 is suitable for being processed by the above-described decoder 100.

Furthermore, the encoder 150 comprises a channel encoding module 170being configured to generate the two or more redundancy bits dependingon the bitstream payload.

FIG. 3 illustrates a system 190 according to an embodiment.

The system 190 comprises the encoder 150 of FIG. 2 for encoding a signalportion of a signal within a frame, wherein the encoder 150 isconfigured to generate the frame so that the frame comprises a bitstreampayload and two or more redundancy bits, wherein the bitstream payloadcomprises a plurality of payload bits, wherein each of the payload bitsexhibits a position within the bitstream payload.

Moreover, the system 190 comprises the decoder 100 of FIG. 1.

In the following, mode decision concepts according to embodiments aredescribed. In particular, mode decision and application of bit-errorconcealment concepts are described.

Some embodiments are based on the finding, that instead of employingfull frame loss concealment, when the signal is non-stationary and thebit-errors appear only in psychoacoustically less important signal data,partial frame loss concealment (PFLC), i.e. concealing only thedistorted data, would be advantageous, since concealment artefacts wouldthen only show up in the psychoacoustically less important part, leadingto a better audio quality.

In some embodiments, to achieve the best audio quality in bit-errorimpaired transmissions, a mode decision is invented to choose betweenFFLC and PFLC. This decision depends on the likelihood of an errorwithin the psychoacoustically more important signal data and the signalcharacteristic of the last and current frame.

The decision, whether to apply full frame loss concealment or partialframe loss concealment is a joint decision of channel coding and sourcecoding:

The channel decoding module proposes to apply:

Full frame loss concealment, if bits in the more sensitive part of thebitstream payload are likely to be corrupt—regardless of the possibilityof errors in the less sensitive part of the bitstream payload.

Partial frame loss concealment, if bits in the more sensitive part ofthe bitstream are likely to be correct, but if bits in the lesssensitive part of the bitstream payload are likely to be corrupt.

The likelihood of a certain part of a bitstream to be corrupt isprovided by the channel decoding module. The channel coding is performedusing block codes. Beside the error correction capability, it alsoprovides a distinct error detection capability. Additionally, individualhashes are derived over the more and the less sensitive part of thebitstream. The evaluation of these hashes provides further certaintyregarding to the aforementioned likelihood.

Source coding, e.g., if the channel coding opts for partial frame lossconcealment, is described in the following.

In an embodiment, the source decoding module 120 may, e.g., beconfigured to select to apply full frame loss concealment,

-   -   if the previous frame was concealed with full frame loss        concealment, or    -   if the highest spectral line in the quantized spectrum        represents a frequency smaller or equal than a threshold        frequency (i.e. 2 kHz) and        -   the stability of the current and last signal is lower than a            given threshold, or        -   a pitch is transmitted (in the more sensitive bitstream            payload) and            -   the highest available spectral line in the quantized                spectrum represents a frequency smaller than the pitch                frequency, or            -   there are relevant peaks in the previous decoded                spectrum part above the highest available spectral line,            -   or        -   no pitch is transmitted (in the more sensitive bitstream            payload) and not enough spectral lines are available in the            quantized spectrum.

In contrast, the source decoding module 120 may, e.g., be configured toselect to apply partial frame loss concealment,

-   -   if the previous frame was not concealed with full frame loss        concealment and        -   if the highest spectral line in the quantized spectrum            represents a frequency higher than a threshold frequency            (i.e. 2 kHz), or        -   if the stability of the current and last signal is higher or            equal than a given threshold and            -   if no pitch is transmitted and at least a certain amount                of spectral lines are available in the quantized                spectrum, or            -   if a pitch is transmitted and the highest available                spectral line in the quantized spectrum represents a                frequency higher than the pitch frequency and there are                no relevant peaks in the previous decoded spectrum part                above the highest available spectral line.

Such embodiments are based on the finding that full-frame pitch-basedconcealment, like time domain concealment, may, e.g., be applied if thesignal is stationary and monophonic (indicated by an available pitch)and the retrieved spectrum is not representative (indicated by at leastone of the two above-mentioned criteria), since under those conditionsit provides in general better results than partial frame lossconcealment.

Partial frame loss concealment may, e.g., be applied if the signal isnon-stationary or polyphonic (indicated by an absent pitch) or if thesignal is stationary and monophonic (indicated by an available pitch)and the retrieved spectrum is representative (indicated by the twoabove-mentioned criteria), since under those conditions it provides ingeneral better results than any full frame loss concealment.

In the following, mode decision concepts according to some embodimentsare described in more detail.

In some embodiments, the part of the bitstream designated for partialframe loss concealment may, e.g., be encoded in multiple code wordsand—in addition—protected, as a whole by a hash value which may, e.g.,be transmitted to the channel decoding module along with the bitstream.Each code may, e.g., have a certain error correction capability. Inembodiments, the channel decoding module may, e.g., first attempt toperform error correction on the designated code words, thereby keepingtrack of the number of corrected symbols for each of them.

In such embodiments, if not all errors were corrected, or if it islikely that not all errors were corrected, then an appropriate errorconcealment mode will be selected and error concealment will beconducted depending on the selected error concealment mode.

In some embodiments, partial frame loss concealment may, e.g., betriggered, if an uncorrectable code word is encountered; or if all codewords were corrected and the re-calculated hash value does not match thereceived hash value.

The latter is for instance the case, if the channel decoding moduleerroneously corrected received code words, which have been damagedbeyond the limits of the error correction capability provided by theunderlying code.

If one of these cases occurs, an analysis of the individual code wordsfollows:

By evaluating the number of corrected symbols for each code word it isdecided, whether a subpart of the part of the bitstream being designatedfor partial frame loss concealment can still be trusted. For this, theprobability of drawing a random word that can be corrected to be a validcode word with the given number of modified symbols is evaluated (whichmay, e.g., be referred to as a risk value). If this probability is abovea certain threshold (e.g. 2^{−16}) (which may, e.g., be referred to as arisk threshold), the corresponding bitstream area is marked as corrupt,otherwise it is treated as correct. This means, that the part indicatedto be concealed with partial frame loss concealment (code words markedas corrupt) shrinks. This leads to a better audio quality, since thebits marked as correct of the part of the bitstream designated forpartial frame loss concealment can be used by the decoder 100 jointlywith the bits of the bitstream representing the psychoacoustically moreimportant signal data.

FIG. 4 illustrates an examples for analysing payload data of code wordsaccording to an embodiment.

In the example of FIG. 4, 16 code words are displayed (numbered 1 to16), where the cross-shaped blocks 210 and 230 correspond to the moresensitive part of the bitstream, while the other blocks (blocks 220,222, 223) correspond to the less sensitive part, designated for partialframe loss concealment. Within the illustrated codewords 7 to 12, thenumbers of corrected symbols are displayed.

It may be assumed that a number of corrected symbols up to “1” leaves anerror detection probability lower than the threshold, and a number ofcorrected symbols higher than “1” leaves an error detection probabilityhigher than the threshold.

In the example of FIG. 4, code words with numbers lower than or equal to“1” are marked as correct (code words 7, 8, 9 and 12:left-bottom-to-right-top-shaped), and the remaining code words, i.e.code words with numbers higher than “1” are marked as corrupt (codewords: 10 and 11: left-top-to-right-bottom-shaped), see FIG. 4. In thegiven example in FIG. 4 this means that the signal part coded inside thecodewords 7, 8, 9 and 12 can still be decoded and only the signal partcoded inside the codewords 10 and 11 has to be concealed by partialframe loss concealment.

In an embodiment, the decoder 100 may, e.g., apply full frame lossconcealment (FFLC if the previous frame was concealed with frame lossconcealment or for the following five events (event 1 to event 5):

Event 1: If bits in the more sensitive part of the bitstream payload arelikely to be corrupt.

Event 2: If the stability of the current and last signal is lower than0.5, in an embodiment for LC3, the stability is given by the stabilityfactor 0 which is calculated as:

$\theta = {1.25 - {\frac{1}{25}{\sum\limits_{k = 0}^{N - 1}\left( {{{scfQ}_{curr}(k)} - {{scfQ}_{prev}(k)}} \right)^{2}}}}$

wherein:

-   -   scfQ_(curr) indicates a scalefactor vector of the current frame,        and    -   scfQ_(prev) indicates a scalefactor vector of the previous frame    -   N indicates the number of scalefactors within the scalefactor        vectors    -   θ indicates a stability factor, which is bounded by 0≤θ≤1    -   k indicates an index for a scalefactor vector

Event 3: If the stability factor is higher or equal to 0.5 and if apitch being sent in the more sensitive bitstream payload and the highestavailable spectral line in the quantized spectrum represents a frequencysmaller than (depending on the employed embodiment): the maximallypossible pitch frequency; or: the pitch frequency sent in the moresensitive bitstream payload.

Event 4: If the stability factor is higher or equal to 0.5 and if apitch being sent in the more sensitive bitstream payload, and k_(be),which is the first spectral bin that could not be recovered in the lesssensitive bitstream payload, is lower than a calculated spectral binindex k_(peak).

This index corresponds to the highest relevant peak in the previousdecoded spectrum and is determined through a peak detector algorithm.The realization of the peak detector is shown in the following examplepseudo code:

function [k_(peak)] = pc_peak_detector({circumflex over (X)}_(prev),N_(F)) block_size = 3; thresh1 = 8; fac = 0.3; mean_block_nrg =mean({circumflex over (X)}_(prev).{circumflex over ( )}2); maxPeak = 0;k_(peak) = 0; if abs({circumflex over (X)}_(prev) ( 0 )) >abs({circumflex over (X)}_(prev)(1))  block_cent = sum({circumflex over(X)}_(prev)(0:1).{circumflex over ( )}2);  if block_cent/block_size >thresh1*mean_block_nrg   cur_max = max(abs({circumflex over(X)}_(prev)(0:1) ) ) ;   next max = max(abs({circumflex over(X)}_(prev)(2:2+block size-1))) ;   if cur_max > next_max    maxPeak =block_cent;    k_(peak) = 1; for k = 0:block_size-1  if abs({circumflexover (X)}_(prev)(k+1)) >= abs({circumflex over (X)}_(prev)(k)) &&abs({circumflex over (X)}_(prev)(k+1)) >= abs({circumflex over(X)}_(prev)(k+2))   block_cent = sum({circumflex over(X)}_(prev)(k:k+block_size-1).{circumflex over ( )}2);   ifblock_cent/block_size > thresh1*mean_block_nrg    cur_max =max(abs({circumflex over (X)}_(prev)(k:k+block_size-1)));    prev_max =0;    for j = k-block_size:k-1     if j > 0      prev_max =max(abs({circumflex over (X)}_(prev)(j)) , prev_max);    next_max =max(abs({circumflex over (X)}_(prev)(k+block_size:k+2*block_size-1)));   if cur_max >= prev_max && cur_max > next_max     if block_cent >fac*maxPeak      k_(peak) = k+block_size-1;      if block_cent >=maxPeak       maxPeak = block_cent; for k =block_size..N_(F)-(2*block_size)  if abs({circumflex over(X)}_(prev)(k+1)) >= abs({circumflex over (X)}_(prev)(k)) &&abs({circumflex over (X)}_(prev)(k+1)) >= abs({circumflex over(X)}_(prev)(k+2))   block_cent = sum({circumflex over(X)}_(prev)(k:k+block_size-1).{circumflex over ( )}2);   ifblock_cent/block_size > thresh1*mean_block_nrg    cur_max =max(abs({circumflex over (X)}_(prev)(k:k+block_size-1))) ;    prev_max =max(abs({circumflex over (X)}_(prev)(k-block_size:k-1)));    next_max =max(abs({circumflex over (X)}_(prev)(k+block_size:k+2*block_size-1)));   if cur_max >= prev_max && cur_max > next_max     if block_cent >fac*maxPeak      k_(peak) = block_size-1;      if block_cent >= maxPeak      maxPeak = block_cent;wherein:

-   -   k indicates a spectral bin,    -   N_(F) indicates the number of spectral lines, and    -   {circumflex over (X)}_(prev) indicates the decoded spectrum of        the last non-FFLC frame.

Event 5: If the stability factor is higher or equal to 0.5, and if nopitch is being sent in the more sensitive bitstream payload and theratio between the partial to the full energy calculated on the lastquantized spectrum is lower than 0.3:

${\sum\limits_{k = 0}^{k_{be} - 1}{(k)^{2}}} < {0.3{\sum\limits_{k = 0}^{N_{F} - 1}{(k)^{2}}}}$

wherein:

-   -   k indicates a spectral bin,    -   k_(be) indicates the first spectral bin which could not be        recovered,    -   N_(F) indicates the number of spectral lines,    -   indicates the quantized spectrum of the last non-FFLC frame.

If none of the five events trigger or the previous frame was notconcealed with full frame loss concealment and the first spectral binwhich could not be recovered is higher than a threshold (i.e.representing a frequency of 2 kHz), partial frame loss concealment(PFLC) should be applied.

The following example pseudo code represents the upper description:

#if 1 /* choose the preferred embodiment by 0 or 1 */ pitchThresholdBin= maxPitchBin; #else pitchThresholdBin = currPitchBin; #endifconcealMode = PFLC; if prevBfi == FFLC;  concealMode = FFLC; else ifk_(be) < bandwidth  if 0 < 0.5   concealMode = FFLC;  else ifpitch_present == 1   k_(peak) = pc_peak_detector({circumflex over(X)}_(prev), NF) ;  if (k_(be) < k_(peak) || k_(be) < pitchThresholdBin)  concealMode = FFLC;  else   part_nrg = sum(

(0:k_(be)-1).{circumflex over ( )}2);   full_nrg = sum(

(0:N_(F)-1).{circumflex over ( )}2);   if (part_nrg < 0.3*full_nrg)   concealMode = FFLC;where:

-   -   prevBfi—indicates the concealment method in the previous frame        if applied    -   concealMode—indicates, whether FFLC or PFLC should be applied    -   pitch_present—indicates, whether a pitch is present in the        current frame    -   pitchThresholdBin—indicates the bin, which needs to be at least        available in order to perform PFLC    -   currPitchBin—indicates the current pitch    -   maxPitchBin—indicates the highest (maximum) pitch value which is        supported    -   bandwidth—indicates the bandwidth bin, which needs to be at        least available in order to not analyze the five conditions    -   k_(be)—first spectral bin which could not be recovered    -   N_(F)—number of spectral lines    -   {circumflex over (X)}_(prev)—decoded spectrum of the last        non-FFLC frame    -   (k)—quantized spectrum of the last non-FFLC frame.

In the following, a Karnaugh-Map for concealment method selectiondepending on source coding is described.

There are five conditions that collectively determine which concealmentmethod should be applied. They are subsequently assigned to logicalvariables are as follows:

a=“The first part of the current bitstream payload does not encode asignal component that is tonal or harmonic”

-   -   b=“The ratio between the energy from 0 to the frequency bin        k_(be)−1 of the previous quantized spectrum and the energy from        0 to the top of the previous quantized spectrum is greater than        or equal to a threshold”    -   c=“The stability factor is higher than or equal to the        threshold”    -   d=“All the frequencies are smaller than pitch frequency or        maximal supported pitch frequency”    -   e=“The previous signal portion encodes at least one peak of the        audio signal being greater than a peak threshold”

Using those variables, a 32(=2⁵) celled-K-map is created as depicted intable 3.

Table 3 illustrates a 32 celled K-map shows graphically the logictriggering either of concealment methods

The corresponding Boolean equations are as follows:

-   -   PFLC (1)=a′cd′e′+abc=c (a′d′e′+ab)    -   FFLC (0)=ab′+c′+a′e+a′d=ab′+c′+a′(e+d)

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, one or more ofthe most important method steps may be executed by such an apparatus.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software or at leastpartially in hardware or at least partially in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitory.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods are performed by any hardware apparatus.

The apparatus described herein may be implemented using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The methods described herein may be performed using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

While this invention has been described in terms of several advantageousembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing the methods andcompositions of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

REFERENCES

[1] “ISO/IEC14496-3 MPEG-4 Information technology—Coding of audio-visualobjects - Part 3: Audio,” 2009.

[2] R. Sperschneider, D. Homm and L.-H. Chambat, “Error Resilient SourceCoding with Differential Variable Length Codes and its Application toMPEG Advance Audio Coding,” in Audio Engineering Societey, Munich, 2002.

[3] E.-m. Oh, H.-s. Sung, K.-h. Choo and J.-h. Kim, “Method andapparatus to conceal error in decoded audio signal”. U.S. Pat. No.8,798,172 B2, 22 Nov. 2007.

[4] P. Lauber and R. Sperschneider, “Error Concealment for CompressedDigital Audio,” in Audio Society, 2001.

1. A decoder for decoding a frame to reconstruct a signal portion of asignal, wherein the signal portion is encoded within the frame, whereinthe frame comprises a bitstream payload and two or more redundancy bits,wherein the bitstream payload comprises a plurality of payload bits,wherein each of the payload bits exhibits a position within thebitstream payload, wherein the decoder comprises: a channel decodingmodule, being configured to detect, depending on the two or moreredundancy bits, whether the bitstream payload comprises one or morecorrupted bits being one or more of the payload bits that are distortedor that are likely to be distorted, a source decoding module, wherein,if the channel decoding module has not detected any corrupted bitswithin the bitstream payload, the source decoding module is configuredto decode the bitstream payload without conducting error concealment toreconstruct the signal portion, wherein, if the channel decoding modulehas detected the one or more corrupted bits within the bitstreampayload, the source decoding module is configured to select a selectederror concealment mode of two or more error concealment modes dependingon the position of at least one of the one or more corrupted bits withinthe bitstream payload and depending on a signal characteristic of thesignal portion of the signal, and is configured to conduct errorconcealment depending on the selected error concealment mode toreconstruct the signal portion.
 2. A decoder according to claim 1,wherein the channel decoding module is an error detection and errorcorrection module being configured to conduct error correction on thebitstream payload before detecting whether the bitstream payloadcomprises the one or more corrupted bits.
 3. A decoder according toclaim 1, wherein a first one of the two or more error concealment modesis a full frame loss concealment mode, wherein, if the channel decodingmodule has indicated that the bitstream payload comprises the one ormore corrupted bits, and if the selected error concealment mode is thefull frame loss concealment mode, the source decoding module isconfigured to conduct error concealment without using the bitstreampayload.
 4. A decoder according to claim 3, wherein a second one of thetwo or more error concealment modes is a partial frame loss concealmentmode, wherein, if the channel decoding module has indicated that thebitstream payload comprises the one or more corrupted bits, and if theselected error concealment mode is the partial frame loss concealmentmode, the source decoding module is configured to obtain the decodedsignal by decoding other bits of the payload bits that are not indicatedby the channel decoding module to be the one or more corrupted bitswithout conducting error concealment on the other bits, and byconducting error concealment on the one or more of the payload bits thatare indicated by the channel decoding module to be the one or morecorrupted bits.
 5. A decoder according to claim 4, wherein the two ormore error concealment modes comprise exactly two error concealmentmodes, wherein a first one of the exactly two error concealment modes isthe full frame loss concealment mode, wherein a second one of theexactly two error concealment modes is the partial frame lossconcealment mode.
 6. A decoder according to claim 4, wherein thebitstream payload is partitioned into a first part of the plurality ofpayload bits of the bitstream payload, and into a second part of theplurality of payload bits of the bitstream payload, wherein, if thechannel decoding module has indicated that the bitstream payloadcomprises the one or more corrupted bits, and if the first part of thebitstream payload comprises at least one of the one or more corruptedbits, the source decoding module is configured to select the full frameloss concealment mode as the selected error concealment mode, andwherein, if the channel decoding module has indicated that the bitstreampayload comprises the one or more corrupted bits, and if the first partof the bitstream payload does not comprise any of the one or morecorrupted bits, the source decoding module is configured to select theselected error concealment mode depending on the signal characteristicof the signal portion of the signal.
 7. A decoder according to claim 6,wherein the frame is a current frame, wherein the bitstream payload is acurrent bitstream payload, wherein the plurality of payload bits is aplurality of current payload bits, wherein the signal portion of thesignal is a current signal portion of the signal, and wherein the signalcharacteristic is a current signal characteristic, wherein, if thechannel decoding module has indicated that the current bitstream payloadcomprises the one or more corrupted bits, the source decoding module isconfigured to select the selected error concealment mode of two or moreerror concealment modes depending on the current signal characteristicof the current signal portion of the signal being encoded by theplurality of current payload bits of the current frame, and depending ona previous signal characteristic of a previous signal portion of thesignal being encoded by a plurality of previous payload bits of aprevious bitstream payload of a previous frame.
 8. A decoder accordingto claim 7, wherein the decoder is an audio decoder, wherein the currentsignal portion of the signal being encoded by the plurality of currentpayload bits of the current bitstream payload is a current audio signalportion of an audio signal, and wherein the previous signal portion ofthe signal being encoded by the plurality of previous payload bits ofthe previous bitstream payload is a previous audio signal portion of theaudio signal wherein the current bitstream payload encodes a pluralityof spectral lines of the current audio signal portion.
 9. A decoderaccording to claim 8, wherein, if the channel decoding module hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module is configured to select the full frame loss concealmentmode as the selected error concealment mode, if the previous frame wasconcealed using full frame loss concealment.
 10. A decoder according toclaim 8, wherein, if the channel decoding module has indicated that thecurrent bitstream payload comprises the one or more corrupted bits, andif the first part of the current bitstream payload does not comprise anyof the one or more corrupted bits, the source decoding module isconfigured to select the full frame loss concealment mode as theselected error concealment mode, if a highest spectral line among theplurality of spectral lines of the current audio signal portion exhibitsa frequency being smaller than or equal to a threshold frequency.
 11. Adecoder according to claim 8, wherein, if the channel decoding modulehas indicated that the current bitstream payload comprises the one ormore corrupted bits, and if the first part of the current bitstreampayload does not comprise any of the one or more corrupted bits, thesource decoding module is configured to select the full frame lossconcealment mode as the selected error concealment mode, if a stabilityfactor is smaller than a predefined threshold, wherein said stabilityfactor indicates a stability of the current audio signal portion and ofthe previous audio signal portion.
 12. A decoder according to claim 8,wherein, if the channel decoding module has indicated that the currentbitstream payload comprises the one or more corrupted bits, and if thefirst part of the current bitstream payload does not comprise any of theone or more corrupted bits, the source decoding module is configured toselect the full frame loss concealment mode as the selected errorconcealment mode, if the previous frame was concealed using full frameloss concealment, or if a stability factor is smaller than a predefinedthreshold, wherein said stability factor indicates a stability of thecurrent audio signal portion and of the previous audio signal portion.13. A decoder according to claim 11, wherein the predefined threshold isequal to 0.5.
 14. A decoder according to claim 8, wherein, if thechannel decoding module has indicated that the current bitstream payloadcomprises the one or more corrupted bits, and if the first part of thecurrent bitstream payload does not comprise any of the one or morecorrupted bits, the source decoding module is configured to select thefull frame loss concealment mode as the selected error concealment mode,if the highest spectral line among the plurality of spectral lines ofthe current audio signal portion exhibits said frequency being smallerthan or equal to said threshold frequency, and if the first part of thecurrent bitstream payload encodes a signal component which is tonal orharmonic, and if the previous signal portion encodes at least one peakof the audio signal being greater than a peak threshold value and whichcorresponds to a frequency being greater than all frequencies beingindicated by the plurality of spectral lines of the current audio signalportion.
 15. A decoder according to claim 14, wherein a pitch of theaudio signal exhibits a pitch frequency, and wherein, if the channeldecoding module has indicated that the current bitstream payloadcomprises the one or more corrupted bits, and if the first part of thecurrent bitstream payload does not comprise any of the one or morecorrupted bits, the source decoding module is configured to select thefull frame loss concealment mode as the selected error concealment mode,if the highest spectral line among the plurality of spectral lines ofthe current audio signal portion exhibits said frequency being smallerthan or equal to said threshold frequency, and if the first part of thecurrent bitstream payload encodes a signal component which is tonal orharmonic, and if all frequencies being indicated by the plurality ofspectral lines of the current audio signal portion are smaller than thepitch frequency; or wherein, if the channel decoding module hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module is configured to select the full frame loss concealmentmode as the selected error concealment mode, if the highest spectralline among the plurality of spectral lines of the current audio signalportion exhibits said frequency being smaller than or equal to saidthreshold frequency, and if the first part of the current bitstreampayload encodes a signal component which is tonal or harmonic, and ifall frequencies being indicated by the plurality of spectral lines ofthe current audio signal portion are smaller than a maximal supportedpitch frequency.
 16. A decoder according to claim 15, wherein, if thechannel decoding module has indicated that the current bitstream payloadcomprises the one or more corrupted bits, and if the first part of thecurrent bitstream payload does not comprise any of the one or morecorrupted bits, the source decoding module is configured to select thefull frame loss concealment mode as the selected error concealment mode,if the highest spectral line among the plurality of spectral lines ofthe current audio signal portion exhibits said frequency being smallerthan or equal to said threshold frequency, and if the first part of thecurrent bitstream payload does not encode a signal component of theaudio signal which is tonal or harmonic, and if the ratio between theenergy from 0 to the frequency bin k_(be)−1 of the previous quantizedspectrum of the previous audio signal to the energy from 0 to the top ofthe previous quantized spectrum of the previous audio signal is smallerthan a ratio threshold, wherein k_(be) is a first spectral bin whichcannot be recovered.
 17. A decoder according to claim 16, wherein theratio threshold is 0.3.
 18. A decoder according to claim 16, wherein, ifthe channel decoding module has indicated that the current bitstreampayload comprises the one or more corrupted bits, and if the first partof the current bitstream payload does not comprise any of the one ormore corrupted bits, the source decoding module is configured to selectthe partial frame loss concealment mode as the selected errorconcealment mode, if the previous frame was not concealed using fullframe loss concealment, and if the highest spectral line among theplurality of spectral lines of the current audio signal portion exhibitsa frequency being greater than said threshold frequency.
 19. A decoderaccording to claim 18, wherein, if the channel decoding module hasindicated that the current bitstream payload comprises the one or morecorrupted bits, and if the first part of the current bitstream payloaddoes not comprise any of the one or more corrupted bits, the sourcedecoding module is configured to select the partial frame lossconcealment mode as the selected error concealment mode, if the previousframe was not concealed using full frame loss concealment, and if thehighest spectral line among the plurality of spectral lines of thecurrent audio signal portion exhibits said frequency being greater thansaid threshold frequency, and if said stability factor is greater thanor equal to said predefined threshold, and if the first part of thecurrent bitstream payload does not encode a signal component of theaudio signal which is tonal or harmonic, and if the ratio between theenergy from 0 to the frequency bin k_(be)−1 of the previous quantizedspectrum of the previous audio signal to the energy from 0 to the top ofthe previous quantized spectrum of the previous audio signal is greaterthan or equal to said ratio threshold.
 20. A decoder according to claim18, wherein, if the channel decoding module has indicated that thecurrent bitstream payload comprises the one or more corrupted bits, andif the first part of the current bitstream payload does not comprise anyof the one or more corrupted bits, the source decoding module isconfigured to select the partial frame loss concealment mode as theselected error concealment mode, if the previous frame was not concealedusing full frame loss concealment, and if the highest spectral lineamong the plurality of spectral lines of the current audio signalportion exhibits said frequency being greater than said thresholdfrequency, and if said stability factor is greater than or equal to saidpredefined threshold, and if the first part of the current bitstreampayload encodes a signal component which is tonal or harmonic, and ifsaid highest spectral line among the plurality of spectral lines of thecurrent audio signal portion exhibits a frequency being greater than thepitch frequency, and if the previous signal portion does not encode anypeak of the audio signal being greater than said peak threshold valueand which corresponds to said frequency being greater than allfrequencies being indicated by the plurality of spectral lines of thecurrent audio signal portion.
 21. A decoder according to claim 8,wherein, if the selected error concealment mode is the partial frameloss concealment mode, the source decoding module is configured todetermine for each code word of a plurality of code words of the secondpart of the bitstream payload, depending on a number of correctedsymbols of said code word, whether or not to conduct error concealmentfor those of the plurality of spectral lines of the current audio signalportion being represented by said code word, and to conduct errorconcealment for said those of the plurality of spectral lines of thecurrent audio signal portion, for which the source decoding module hasdetermined that error concealment shall be conducted.
 22. A decoderaccording to claim 21, wherein, for each code word of a plurality ofcode words of the second part of the bitstream payload, the sourcedecoding module is configured to determine a risk value indicating anapproximation of a probability that said code word is corrupt, and todetermine whether or not said risk value is greater than a riskthreshold.
 23. A decoder according to claim 21, wherein, if said riskvalue is greater than said risk threshold, the source decoding module isconfigured to conduct error concealment for those of the plurality ofspectral lines of the current audio signal portion being represented bysaid code word.
 24. A decoder according to claim 23, wherein the riskthreshold is 2⁻¹⁶.
 25. A decoder according to claim 21, wherein thesource decoding module is configured to conduct said error concealmentfor said code word in the partial frame loss error concealment mode. 26.A decoder according to claim 1, wherein the channel decoding module isconfigured to detect that the bitstream payload comprises one or morecorrupted bits, if the channel decoding module encounters anuncorrectable code word within the bitstream payload and/or if thechannel decoding module, after conducting error correction on aplurality of code words of the bitstream payload, determines are-calculated hash value, which depends on said plurality of code wordsafter the error correction, that differs from a received hash value. 27.A system, comprising: an encoder for encoding a signal portion of asignal within a frame, wherein the encoder is configured to generate theframe so that the frame comprises a bitstream payload and two or moreredundancy bits, wherein the bitstream payload comprises a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, and a decoder according to claim
 1. 28. Anencoder, comprising: a source encoding module for encoding a signalportion of a signal within a frame, wherein the source encoding moduleis configured to generate the frame so that the frame comprises abitstream payload and two or more redundancy bits, wherein the bitstreampayload comprises a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, whereinthe frame being generated by the source encoding module is suitable forbeing processed by the decoder according to claim 1, and a channelencoding module being configured to generate the two or more redundancybits depending on the bitstream payload.
 29. A method for decoding aframe to reconstruct a signal portion of a signal, wherein the signalportion is encoded within the frame, wherein the frame comprises abitstream payload and two or more redundancy bits, wherein the bitstreampayload comprises a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, whereinthe method comprises: detecting, depending on the two or more redundancybits, whether the bitstream payload comprises one or more corrupted bitsbeing one or more of the payload bits that are distorted or that arelikely to be distorted, if no corrupted bits have been detected withinthe bitstream payload, decoding the bitstream payload without conductingerror concealment to reconstruct the signal portion, and if one or morecorrupted bits have been detected within the bitstream payload,selecting a selected error concealment mode of two or more errorconcealment modes depending on the position of at least one of the oneor more corrupted bits within the bitstream payload and depending on asignal characteristic of the signal portion of the signal, andconducting error concealment depending on the selected error concealmentmode to reconstruct the signal portion.
 30. A method, comprising:encoding a signal portion of a signal within a frame, wherein the frameis generated so that the frame comprises a bitstream payload and two ormore redundancy bits, wherein the bitstream payload comprises aplurality of payload bits, wherein each of the payload bits exhibits aposition within the bitstream payload, and conducting the method fordecoding a frame to reconstruct a signal portion of a signal, whereinthe signal portion is encoded within the frame, wherein the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload, wherein the method comprises: detecting, depending on the twoor more redundancy bits, whether the bitstream payload comprises one ormore corrupted bits being one or more of the payload bits that aredistorted or that are likely to be distorted, if no corrupted bits havebeen detected within the bitstream payload, decoding the bitstreampayload without conducting error concealment to reconstruct the signalportion, and if one or more corrupted bits have been detected within thebitstream payload, selecting a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and conducting error concealment depending on the selected errorconcealment mode to reconstruct the signal portion, using the frame. 31.A method for encoding a signal portion of a signal within a frame,wherein the method comprises: generating the frame so that the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload, wherein the frame is suitable for being decoded by the methodfor decoding a frame to reconstruct a signal portion of a signal,wherein the signal portion is encoded within the frame, wherein theframe comprises a bitstream payload and two or more redundancy bits,wherein the bitstream payload comprises a plurality of payload bits,wherein each of the payload bits exhibits a position within thebitstream payload, wherein the method comprises: detecting, depending onthe two or more redundancy bits, whether the bitstream payload comprisesone or more corrupted bits being one or more of the payload bits thatare distorted or that are likely to be distorted, if no corrupted bitshave been detected within the bitstream payload, decoding the bitstreampayload without conducting error concealment to reconstruct the signalportion, and if one or more corrupted bits have been detected within thebitstream payload, selecting a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and conducting error concealment depending on the selected errorconcealment mode to reconstruct the signal portion, and generating thetwo or more redundancy bits depending on the bitstream payload.
 32. Anon-transitory digital storage medium having a computer program storedthereon to perform the method decoding a frame to reconstruct a signalportion of a signal, wherein the signal portion is encoded within theframe, wherein the frame comprises a bitstream payload and two or moreredundancy bits, wherein the bitstream payload comprises a plurality ofpayload bits, wherein each of the payload bits exhibits a positionwithin the bitstream payload, wherein the method comprises: detecting,depending on the two or more redundancy bits, whether the bitstreampayload comprises one or more corrupted bits being one or more of thepayload bits that are distorted or that are likely to be distorted, ifno corrupted bits have been detected within the bitstream payload,decoding the bitstream payload without conducting error concealment toreconstruct the signal portion, and if one or more corrupted bits havebeen detected within the bitstream payload, selecting a selected errorconcealment mode of two or more error concealment modes depending on theposition of at least one of the one or more corrupted bits within thebitstream payload and depending on a signal characteristic of the signalportion of the signal, and conducting error concealment depending on theselected error concealment mode to reconstruct the signal portion, whensaid computer program is run by a computer.
 33. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod, the method comprising: encoding a signal portion of a signalwithin a frame, wherein the frame is generated so that the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload, and conducting the method for decoding a frame to reconstruct asignal portion of a signal, wherein the signal portion is encoded withinthe frame, wherein the frame comprises a bitstream payload and two ormore redundancy bits, wherein the bitstream payload comprises aplurality of payload bits, wherein each of the payload bits exhibits aposition within the bitstream payload, wherein the method comprises:detecting, depending on the two or more redundancy bits, whether thebitstream payload comprises one or more corrupted bits being one or moreof the payload bits that are distorted or that are likely to bedistorted, if no corrupted bits have been detected within the bitstreampayload, decoding the bitstream payload without conducting errorconcealment to reconstruct the signal portion, and if one or morecorrupted bits have been detected within the bitstream payload,selecting a selected error concealment mode of two or more errorconcealment modes depending on the position of at least one of the oneor more corrupted bits within the bitstream payload and depending on asignal characteristic of the signal portion of the signal, andconducting error concealment depending on the selected error concealmentmode to reconstruct the signal portion, using the frame, when saidcomputer program is run by a computer.
 34. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for encoding a signal portion of a signal within a frame, whereinthe method comprises: generating the frame so that the frame comprises abitstream payload and two or more redundancy bits, wherein the bitstreampayload comprises a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, whereinthe frame is suitable for being decoded by the method for decoding aframe to reconstruct a signal portion of a signal, wherein the signalportion is encoded within the frame, wherein the frame comprises abitstream payload and two or more redundancy bits, wherein the bitstreampayload comprises a plurality of payload bits, wherein each of thepayload bits exhibits a position within the bitstream payload, whereinthe method comprises: detecting, depending on the two or more redundancybits, whether the bitstream payload comprises one or more corrupted bitsbeing one or more of the payload bits that are distorted or that arelikely to be distorted, if no corrupted bits have been detected withinthe bitstream payload, decoding the bitstream payload without conductingerror concealment to reconstruct the signal portion, and if one or morecorrupted bits have been detected within the bitstream payload,selecting a selected error concealment mode of two or more errorconcealment modes depending on the position of at least one of the oneor more corrupted bits within the bitstream payload and depending on asignal characteristic of the signal portion of the signal, andconducting error concealment depending on the selected error concealmentmode to reconstruct the signal portion, and generating the two or moreredundancy bits depending on the bitstream payload, when said computerprogram is run by a computer.
 35. A frame being generated according tothe method for encoding a signal portion of a signal within a frame,wherein the method comprises: generating the frame so that the framecomprises a bitstream payload and two or more redundancy bits, whereinthe bitstream payload comprises a plurality of payload bits, whereineach of the payload bits exhibits a position within the bitstreampayload, wherein the frame is suitable for being decoded by the methodfor decoding a frame to reconstruct a signal portion of a signal,wherein the signal portion is encoded within the frame, wherein theframe comprises a bitstream payload and two or more redundancy bits,wherein the bitstream payload comprises a plurality of payload bits,wherein each of the payload bits exhibits a position within thebitstream payload, wherein the method comprises: detecting, depending onthe two or more redundancy bits, whether the bitstream payload comprisesone or more corrupted bits being one or more of the payload bits thatare distorted or that are likely to be distorted, if no corrupted bitshave been detected within the bitstream payload, decoding the bitstreampayload without conducting error concealment to reconstruct the signalportion, and if one or more corrupted bits have been detected within thebitstream payload, selecting a selected error concealment mode of two ormore error concealment modes depending on the position of at least oneof the one or more corrupted bits within the bitstream payload anddepending on a signal characteristic of the signal portion of thesignal, and conducting error concealment depending on the selected errorconcealment mode to reconstruct the signal portion, and generating thetwo or more redundancy bits depending on the bitstream payload.